In the context of spatial databases, the defined space in which geometries are described is called a spatial reference system (SRS). A spatial reference system defines, at minimum:

Units of measure of the underlying coordinate system (degrees, meters, and so on)

Maximum and minimum coordinates (also referred to as the bounds)

Default linear unit of measure

Whether the data is planar or spheroid data

Projection information for transforming the data to other SRSs

Every spatial reference system has an identifier called a Spatial Reference Identifier (SRID). When SQL Anywhere performs operations like finding out if a geometry touches another geometry, it uses the SRID to look
up the spatial reference system definition so that it can perform the calculations properly for that spatial reference system.
In a SQL Anywhere database, each SRID must be unique.

By default, SQL Anywhere adds the following spatial reference systems to a new database:

Default - SRID 0
This is the default spatial reference system used when constructing a geometry and the SRID is not specified in the
SQL and is not present in the value being loaded.

Default is a Cartesian spatial reference system that works with data on a flat, two dimensional plane. Any point on the plane
can be defined using a single pair of x, y coordinates where x and y have the bounds -1,000,000 to 1,000,000. Distances are
measured using perpendicular coordinate axis. This spatial reference system is assigned SRID of 0.

Cartesian is a planar type of spatial reference system.

WGS 84 - SRID 4326
The WGS 84 standard provides a spheroidal reference surface for the Earth. It is the spatial reference system used by
the Global Positioning System (GPS). The coordinate origin of WGS 84 is the Earth's center, and is considered accurate up
to ±1 meter. WGS stands for World Geodetic System.

WGS 84 Coordinates are in degrees, where the first coordinate is longitude with bounds -180 to 180, and the second coordinate
is latitude with bounds -90 to 90.

The default unit of measure for WGS 84 is METRE, and it is a round-Earth type of spatial reference system.

WGS 84 (planar) - SRID 1000004326
WGS 84 (planar) is similar to WGS 84 except that it uses equirectangular projection, which distorts length, area and
other computations. For example, at the equator in both SRID 4326 and 1000004326, 1 degree longitude is approximately 111
km. At 80 degrees north, 1 degree of longitude is approximately 19 km in SRID 4326, but SRID 1000004326 treats 1 degree of
longitude as approximately 111 km at all latitudes. The amount of distortion of lengths in the SRID 1000004326 is considerable—off by a factor of 10 or more—the distortion
factor varies depending on the location of the geometries relative to the equator. Consequently, SRID 1000004326 should not
be used for distance and area calculations. It should only be used for relationship predicates such as ST_Contains, ST_Touches,
ST_Covers, and so on.

The default unit of measure for WGS 84 (planar) is DEGREE, and it is a flat-Earth type of spatial reference system.

Since you can define a spatial reference system however you want and can assign any SRID number, the spatial reference system
definition (projection, coordinate system, and so on) must accompany the data as it moves between databases or is converted
to other SRSs. For example, when you unload spatial data to WKT, the definition for the spatial reference system is included
at the beginning of the file.

SQL Anywhere also provides thousands of predefined SRSs for use. However, these SRSs are not installed in the database by
default when you create a new database. You use the sa_install_feature system procedure to add them. See sa_install_feature system procedure.

Spatial reference system information is stored in the ISYSSPATIALREFERENCESYSTEM system table. The SRIDs for the SRSs are
used as primary key values in this table. The database server uses SRID values to look up the configuration information for
a spatial reference system so that it can interpret the otherwise abstract spatial coordinates as real positions on the Earth.

Some popular web mapping and visualization applications such as Google Earth, Bing Maps, and ArcGIS Online, use a spatial
reference system with a Mercator projection that is based on a spherical model of the Earth. This spherical model ignores
the flattening at the Earth's poles and can lead to errors of up to 800m in position and up to 0.7 percent in scale, but it
also allows applications to perform projections more efficiently.

In the past, commercial applications assigned SRID 900913 to this spatial reference system. However, EPSG has since released
this projection as SRID 3857. For compatibility with applications requiring 900913, you can do the following:

Use the sa_install_feature system procedure to install all of the spatial reference systems provided by SQL Anywhere (including
SRID 3857).

Perform dbunload -n to get the 3857 SRID definition.

Use Sybase Central to create a spatial reference system with SRID 900913 using the information from the unloaded SRID definition.